CH. x.] NATURAL SELECTION. 11 



crease; but when we consider the reproductive capacity of 

 insects and plants, the nails in the horse s shoe are left no 

 where. When Arctic travellers tell us that the minute proto- 

 coccus multiplies so fast as to colour blood-red many acres 

 of snow in a single night, such a rate of increase appears 

 astonishing. But it is a mere trifle compared to what would 

 happen if reproduction were to go on unchecked. Let us 

 take the case of a plant which yields one hundred seeds 

 yearly, and suppose each of these seeds to reach maturity so 

 as to yield its hundred offspring in the following year : in the 

 tenth year the product would be one hundred quintillions 1 

 of adult plants ! As this is one of those figures before which 

 the imagination stands hopelessly baffled, let us try the effect 

 of an illustration. Supposing each of these plants to be from 

 three to five inches in length, so that about twenty thousand 

 would reach an English mile, the total length of the number 

 just mentioned would be equal to five million times the radius 

 of the earth s orbit. The ray of light, which travels from the 

 sun to the earth in eight minutes, would be seventy-six years 

 in passing along this line of little plants I And in similar 

 wise, it might be shown of many insects, crustaceans, and 

 fishes, that their unchecked reproduction could not long go 

 on without requiring the assimilation of a greater quantity 

 of matter than is contained in the whole solar system. 



We may now begin dimly to realize how prodigious is the 

 slaughter which unceasingly goes on throughout the organic 

 world. For obviously, when a plant, like the one just cited, 

 maintains year by year a tolerable uniformity in its numbers, 

 it does so only because on the average ninety-nine seeds 

 perish prematurely for one that survives long enough to 

 produce other seeds. A single codfish has been known to 

 lay six million eggs within a year. If these eggs were all 

 to become adult codfishes, and the multiplication were to 



1 According to the American system of numeration. One hundred thousand 

 trillions, according to the English system. 



